The purpose of this protocol is to determine the chromosomal locus or loci of the genes responsible for hypertrophic cardiomyopathy (HCM). This heart disease is of obscure etiology and may range in its presentation from an incidental finding to sudden death. The gold standard in the diagnosis of HCM remains echocardiography. Approximately one-half of the cases are sporadic and one-half are familial. Previous family studies have suggested an autosomal dominant pattern of inheritance in familial cases. We have ascertained two large kindreds affected with the disease. An autosomal dominant pattern of inheritance is evident in both pedigrees. We are currently studying portions of both families with echocardiography while we collect blood for DNA extraction and blood protein polymorphisms determinations. This will allow us to use the technique to genetic linkage analysis to map the gene. This technique has been already used by others to map the genes responsible for diseases such as cystic fibrosis, Huntington's Chorea, Alzheimers disease and bipolar affective disorder. Once the gene has been localized questions of genetic heterogeneity can be addressed by studying patients outside of these two families. Ultimately the marker which establishes the chromosomal location can be used to obtain the gene itself.